Effect of wider rear wheel

Please share your secrets! What mods have you made to your TRX?

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Tarwetijger
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Effect of wider rear wheel

Post by Tarwetijger » Mon Oct 26, 2009 9:53 pm

Since there are a few here with track experience on a TRX, I would like the know your opinions about this. It needs some introduction though.

I fitted a YZF swingarm to my TRX, so I could use the magnesium rims I already had. The point is, this rear rim is 6 inch wide. The original YZF rim is 5,5", the original TRXs is 5". The tyresizes are correspondig to this, so 160 on original rims for the TRX, the YZF uses 180 rear tyres. The magnesium rim runs best with a 190 tyre, because a 180 is not round enough.
Because of the weight benefits, I use the magnesium rims during track days, so i'm using 190 tyres (supercorsas or pilot powers). On the street I put the original YZF rims in with a 180 rear tyre (pilot road 2, in order to make a decent number of km's before I have to change tyres, again...).

Are you still with me? Okay. Now, I have noticed that the TRX runs wide very easily during track days. I thought it was just me, putting on the throttle to early. But I cant help thinking the bike didn't act like this this before the modifications (putting in YZF frontend and swingarm)! It really looks like I have to add more lean angle then someone that is just in front of me, riding at (more or less) the same speed on whatever bike!

Now I'm reading this book: Motorcycle Design and Technology, by Gaetano Cocco. It handles exciting stuff, but now i'm reading in chapter 4 - control of the motorcycle when cornering, after some equations:
"As a result of this, the bigger the crosssection of the tire, and equally, the greater the speed at which you enter the corner, the more you must lean the bike into the curve. "
So this complies with the feeling I already had: changing the rear rim to a light weight but wider one, maybe wasn't a very good idea... But it gets worse later on:
"We hope these observations will have convinced you to be rather cautious about substituting your original tires and rims with bigger sized replacements".
So there, it says it all!
Now I'm really in doubt what to do. What are the options?
- just use the magnesium rim because its cool err I meant lighter! And go slower through the corners...
- use the 5,5" YZF rim also on trackdays, like a compromise. Now I think of it, I think the 190 tyre is even worse then the 180.
- get the 5" TRX rim fitted in the YZF swingarm
- get rid of YZF swingarm and use the original one with 5" rim.

Keep in mind though that the ability to change wheels (tires) for road use and trackdays is really nice.
I would like to know your thoughts on this issue!

Edit: in case you were wondering: yes, a 6" rim with 190 tyre fits in. But it's tight. It also appeared to depend on the tyre itself, a 190 michelin pilot power is actually a tiny bit wider then a 190 pirelli supercorsa. The michelin touches the chain every now and then :oops:, the pirelly doesn't.

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Re: Effect of wider rear wheel

Post by trixynut » Mon Oct 26, 2009 11:22 pm

Interesting problem and I dunno the solution but:

Which GP bikes carry the most corner speed? 125's
How wide are their rear tyres? not very.

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Re: Effect of wider rear wheel

Post by M.V. » Tue Oct 27, 2009 12:27 am

trixynut wrote:Interesting problem and I dunno the solution but:

Which GP bikes carry the most corner speed? 125's
How wide are their rear tyres? not very.
They're also a LOT lighter! But very true, Once you past a certain width, I think it's a waste of rubber!

Also, I presume Yamaha would know the best combination, even if the old TRX was a parts bin special! :wink:

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Re: Effect of wider rear wheel

Post by Tarwetijger » Tue Oct 27, 2009 10:19 am

But I've seen a lot of modifications on TRXs, especially on this forum. Frontends, swingarms, wheels - everything is swapped for something that is supposed to be better. But is it? Even just by putting shorter dogbones, to raise the rear, the rake is altered. You can guess what Cocco has to say about that!
The same accounts for lowering the front (forks sticking through the yokes), which almost everyone has done to his/her TRX!

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Re: Effect of wider rear wheel

Post by trixynut » Tue Oct 27, 2009 10:33 am

I think the point is that the TRX is a bit of a compromise bike: sportsbike and tourer with nothing too extreme, so it can stand a bit of alteration if your main aim is to ride it in a spirited way. plus things like the yzf swinger, wheel, forks etc as standard would have added to the initial cost to buy.

The bike and its geometry was, however, designed around a 5 in. rear with a 160/60 tyre.

As for a bigger rear wheel and tyre, yes the yzf 5.5in rim looks trick, but its not really needed: gives a bigger contact patch but trx's are not overwhelmed with power, even if tuned to the 100bhp max.

Same applies to the YZF swinger: there's no way even a tuned TRX makes enough power to flex the standard swinger enough for it to need the extra bracing thats on the YZF item, but it looks cool!

A bigger wheel and tyre is usually heavier and had more gyroscopic forces, making the bike less 'flickable'. I have a mate who races SV650's which run 160 and 120 tyres and he is never short of grip! 160 120 is a standard supermoto combination too.

180 or 190 rear raises the back end up a bit (bigger diameter) so a slight advantage there but....?

How does a 190 on a magnesium rim compare to a 160 on a standard rim weight-wise?

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Re: Effect of wider rear wheel

Post by Tarwetijger » Tue Oct 27, 2009 10:56 am

All true, Trixynut.

Here are the weights in kg:

swingarm
TRX: 4,4
YZF: 5,5

Wheels (including tyres, discs and/or sprocket) - front | rear
TRX : 11,9 | 14,7
YZF : 12,2 | 15,9
Marvic: 9,8 | 12,9

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Re: Effect of wider rear wheel

Post by Tarwetijger » Tue Oct 27, 2009 11:18 am

I would like to know from other track-riders which rear tire they use? Since I'm obviously not the only one with a YZF swingarm.

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Re: Effect of wider rear wheel

Post by HansJ » Tue Oct 27, 2009 4:31 pm

I have the YZF swing-arm, and used to have the YZF rear wheel (5.5"). I actually never rode the bike with the original rim, as the YZF parts where on the bike when I bought it. Opinions is something I have though ;) I have always had 180/55 on the rear though, and always street rubber, at the moment Sportec M3s.

Ligther rims means more flickable, improved suspension (should at least) and better acceleration (in theory). I think You save some plus points there in comparison with the YZF setup.

Having around 100 BHP myself, I have not yet lacked rubber, in the sense that the rear is stepping out when accelerating. (I am probably still too bad a driver though, another guy who used to be extremely fast on a bog standard TRX said after a test-run with mine at a track : "I guess one could put some nice black lines on the tarmac with that")

Grip/lean angle also has to do (as You're probably perfectly aware of) with what type of track and above all, rider style. If You can improve on not just getting the knee and the arse off the bike, but get the whole upper body, this will give more ground clearance (if that's the issue?)

Running wide, is the bike "pushing" the front causing You to go wide, or? It could be something with suspension settings as well. A lighter package will probably need some adjustments.

Don't know if this made You any wiser...

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Re: Effect of wider rear wheel

Post by Tarwetijger » Tue Oct 27, 2009 4:51 pm

HansJ wrote: 1. I have the YZF swing-arm, and used to have the YZF rear wheel (5.5"). I actually never rode the bike with the original rim, as the YZF parts where on the bike when I bought it. Opinions is something I have though ;) I have always had 180/55 on the rear though, and always street rubber, at the moment Sportec M3s.

2. Ligther rims means more flickable, improved suspension (should at least) and better acceleration (in theory). I think You save some plus points there in comparison with the YZF setup.

3. Having around 100 BHP myself, I have not yet lacked rubber, in the sense that the rear is stepping out when accelerating. (I am probably still too bad a driver though, another guy who used to be extremely fast on a bog standard TRX said after a test-run with mine at a track : "I guess one could put some nice black lines on the tarmac with that")

4. Grip/lean angle also has to do (as You're probably perfectly aware of) with what type of track and above all, rider style. If You can improve on not just getting the knee and the arse off the bike, but get the whole upper body, this will give more ground clearance (if that's the issue?)

5. Running wide, is the bike "pushing" the front causing You to go wide, or? It could be something with suspension settings as well. A lighter package will probably need some adjustments.

6. Don't know if this made You any wiser...
1. Do I understand correctly that you are not using the YZF wheel (5,5") anymore? If so, what are you running now?
2. Exactly the reason why I would like to use the magn. rims!
3. It is not that I think I really need a 190 tire, it just of the reasons you mentioned at ad 2.
4. Yes, ground clearance is the issue, as I see guys in front of me that literally need less lean angle at the same speed. It's really frustrating if you take in account that we TRX riders need the corners in order to keep up with the big bhp bikes.
I don't think that hanging off is the problem, as I'm already trying that very hard! It is not my intention to flaunt here, but see below. :)
5. I don't think that's the reason, because of ad 4.
6. I don't know either :P
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Re: Effect of wider rear wheel

Post by HansJ » Tue Oct 27, 2009 6:55 pm

Tarwetijger wrote:1. Do I understand correctly that you are not using the YZF wheel (5,5") anymore? If so, what are you running now?
2. Exactly the reason why I would like to use the magn. rims!
3. It is not that I think I really need a 190 tire, it just of the reasons you mentioned at ad 2.
4. Yes, ground clearance is the issue, as I see guys in front of me that literally need less lean angle at the same speed. It's really frustrating if you take in account that we TRX riders need the corners in order to keep up with the big bhp bikes.
I don't think that hanging off is the problem, as I'm already trying that very hard! It is not my intention to flaunt here, but see below. :)
5. I don't think that's the reason, because of ad 4.
6. I don't know either :P
Image
1, Oh, I thought you remembered, we had a discussion about it some time ago. I'm a brother in arms, also have Marvic 3 spoke rims, but 5.5.

2, Same as me then :)

3, Agree, and didn't imply that you thought differently. On the other hand, more rubber on the ground would also allow for higher side forces, instead of acceleration forces, or?

4, OK, that looks like a textbook example of good hanging-off! =D> There are so many guys just trying to get the knee down, and hang off only with the arse and the knee. (I have a mate that is quite fast on the track, and he has never used his knee-sliders, passing many guys with well-scruffed sliders... All he does is using his upper body when hanging off.)

Another thought, if You compare with modern bikes that have a much lower CoG, they will lean less in comparison with TRXs (or am i thinking completely wrong here?) Do you touch ground with the pegs, and if so, do you have other pegs mounted already? Maybe the extra rubber, plus the extra width 8(that becomes height when leaned over) will help you here, being an argument for keeping the 190s I mean :lol: Are you running wide because the pegs touch down, or?

5, OK, if You're convinced, then I am as well :)

6, At a best, confused but on a higher level then

To sum it all up, I don't know if the advantages with 180/190 are being outweighed by the disadvantages,and no clue whatsoever if the difference between 180 and 190 is that immense.I have heard guys down-sizing from 190 though. I don't know how the rim-width affects geometry and steering. On the other hand, the Marvic rims gives advantages also. Tricky...
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Re: Effect of wider rear wheel

Post by Tarwetijger » Wed Oct 28, 2009 9:45 am

HansJ: Ah, of course, you 're the other Marvic man! My bad. You're lucky though, having a 5,5".
Pegs did touch the ground occasionally, but not anymore since I replaced them. But now it is possible to scratch the sidestand on the ground! :o Before the pegs touched, I scraped a lot of material of my boots. Which scared my wife to death, she tought I would scrape my own toes in the end! 8-[

Anyway, I think I will look and see if I can use the 5" (TRX) rim in the YZF swingarm. Especially for tight tracks that might be useful. The 5,5" is fine for streetuse.

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Re: Effect of wider rear wheel

Post by HansJ » Wed Oct 28, 2009 9:55 am

Tarwetijger wrote:HansJ: Ah, of course, you 're the other Marvic man! My bad. You're lucky though, having a 5,5".
Pegs did touch the ground occasionally, but not anymore since I replaced them. But now it is possible to scratch the sidestand on the ground! :o Before the pegs touched, I scraped a lot of material of my boots. Which scared my wife to death, she tought I would scrape my own toes in the end! 8-[

Anyway, I think I will look and see if I can use the 5" (TRX) rim in the YZF swingarm. Especially for tight tracks that might be useful. The 5,5" is fine for streetuse.
I've been sleepless tonight :)

What do You actually mean by running wide? Is it when turning in, in the apex, or when You're accelerating?

Generally speaking, wider means slower turning in, and this means either that you'll be finished turning in later, and needing more leaning, or that You'll have a wider radius and have to start turning in earlier and be finished with the curve later. (I admit I am speculating a bit here, don't take these words as "the one and only truth"...) This could be "solved" by using more force in the turning in, i.e. that you'll have to compensate with your muscles to get the same turning point, radius and leaning angle?
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Re: Effect of wider rear wheel

Post by Tarwetijger » Wed Oct 28, 2009 1:51 pm

Yes, I have to use more force (then I normally would or more then expected) on the clipons (i.e. stronger countersteering) to get the line I want.
I have to work harder to get the cornering line tight enough. This feels really unnatural! Imagine it like you can't predict the line trough the corners accurate enough. Because normally, it's like: braking, turn in late, drag the knee and go on the throttle! It is just this that I like(d) so much about the TRX (it is/was far more easy to take corners very quickly with the TRX then with my former YZF750 for example). It kinda feels like I have ruined this with all my - so-called - modifications. :x
And yes, it could be solved with a more slowly corner entrance, but that's not the point of track riding, is it? #-o

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Re: Effect of wider rear wheel

Post by HansJ » Wed Oct 28, 2009 2:51 pm

Ok, so it's basically turning in that's slower.Now that fits with the width.As Isaid earlier, I've heard guys on 1 litre IL4s going down to 180 to improve turning in speeds, so if this is bothering you that much, it seems there's only one way to go (unless altering rideheight front/back is an option any longer.)

The slower entrance speed could be a winning concept though (to a certain point only). Accelerating before apex will surprise many an IL4 driver :D
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Re: Effect of wider rear wheel

Post by Trixz » Thu Oct 29, 2009 12:18 pm

Tarwetijger wrote:Since there are a few here with track experience on a TRX, I would like the know your opinions about this. It needs some introduction though.....the pirelly doesn't.....
It's Pirelli :roll:

:lol:
trixynut wrote:As for a bigger rear wheel and tyre, yes the yzf 5.5in rim looks trick, but its not really needed: gives a bigger contact patch but trx's are not overwhelmed with power, even if tuned to the 100bhp max.

Same applies to the YZF swinger: there's no way even a tuned TRX makes enough power to flex the standard swinger enough for it to need the extra bracing thats on the YZF item, but it looks cool!
Can't agree more Image

I run a PVM 5,5 rim with the 160-60 tyre, and it runs lovely on twisty bends. Dunno for the track as of yet, hopefully in 2010 Image
Tarwetijger wrote:But now it is possible to scratch the sidestand on the ground!
[-X on a track-rim TRX ...


Knowing your 'problem' now, I must agree that it's pointing @ your wider rim, and all the negative specs that others already have stated about this, would say so!

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Gerben
Former TRX rider ...former TRX of The Month owner June 2007 ánd May 2009... -and RC51 track bike *and crashing it* past-owner-

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