Effect of wider rear wheel

[punica78]

The application of a YZF front and back-end on the TRX has been applied many times in the past. I've even seen some articles of magazines about it which stated that it was an improvement. As for me I've done the swap because I wanted more stability on my TRX. I always understood that the wider your wheel, the more stability you get in turns and it gives a larger surface for braking and acceleration.
Off course there are some downsides to wider tyres but since riding a motorcycle is a personal experience everyone should decide whether he/she wants a 160 or a 180. Changing the original set-up of a bike brings along some risks of diminishing your bike but also the chance for optimizing, either way it's a calculated guess in my opinion.

Never the less, this topic is interesting to read how others have experienced certain mods.

[dandywarhol]

Good question... and here's where my technical knowledge gets a bit shakey...

If you rode my bike you would not consider it to be overdamped at all... it's actually reasonably plush in terms of damping, so it's not just a case of winding the damping up harder. That would be counterproductive. I'm a big fan of fitting the right springs and then running the least amount of damping possible to get the thing to ride well. IMO overdamping is often done by people who are trying to make the bike feel "stiffer". But using extra damping to overcome too soft springs just stops the suspension from doing what it's supposed to do... move. So I started with fitting the right springs and then gradually winding up the damping (both compression and rebound) until it reached a point where it was controlling the movement of the suspension the way I want. Afterall, that is the job of the damping function... to control the movement of the suspension... not to override it.

As for the changes that were made to my shock to stop it squatting, I'm not totally up on the technical terms, but it was a bit more than just revalving the rebound damping circuit (I think). The way my tuner described it was to think of it like an extra rebound damping circuit, which doesn't affect the suspension at all over normal bumps, but under long slow continuous compression (such as you get when it squats under power) it will come into play and stop the suspension from getting bogged down. I don't understand the mechanical side of what he actually did to the shock internals, but he definitely described it as though it operated as another rebound circuit. Having said that, it's not like I have an extra rebound control or anything, so it may just be a case of revalving, but he described it as an extra valve or circuit. Perhaps those on here more technically minded than I might have a better idea of what I'm describing than me. It's also worth remembering that my suspension guy is one of the best in Oz, so he may be a little more advanced in his knowledge than most people (and fair enough too).

All I know is that whatever he did worked a treat. I can tighten the line of the bike easily midcorner if necessary and it's even capable of a totally different riding style now. TRX's are known for good turn in and mid corner speed, but mine can also be ridden hard by dragging it to the apex still heavy on the brakes, turning it hard and sharp at a lower speed, then getting on the gas as hard as you please and firing it off the exit on a tight exit line... it will hold a tight line on exit pretty much no matter what you do. Works even better on switchbacks or "S" bends where you want a tight exit from the first bend to set up your line for a fast and wide exit out of the second bend.

Anyway... I have a track day coming up early december, so I'll report back on how it goes on a racetrack with the changes. I think I will find it still a bit soft for track work, but it is mostly a road bike 98% of the time, so I want it to remain road biased.

Sounds like he's talking about 2 stage COMPRESSION damping. This has low sped control for undulating kind of bumps/squat and high speed for harsh, pothole kind of bumps - th high and low speed are to do with the speed of the shock piston, not the bike.

This is what Race Tech emulators do in their front fork conversion

[Beau]

Something along those lines... but it's not quite that advanced.

[Beau]

Beau, interesting findings! I thought the same as Honk, that the rear extends while accelerating.

I think you'll find it does

the simplest way of illustrating this is to push your bike up against a brick wall (or apply the front brake), wind on some revs and relese the clutch lever - as if strating a burn out.

Have a look at what the rear of the bike does

True... but pushing it up against a wall is entirely different to how it will react under load in a corner. You need to remember that the geometry will change under cornering forces and then it wll be in a state where the swingarm angle will indeed cause it to squat. You're also ignoring weight transferance.

Rule of thumb... chain drives squat, shaft drives lift. My TRX has a chain and it squats. Or at least it used to.

[phuk72]

Beau, interesting findings! I thought the same as Honk, that the rear extends while accelerating.

I think you'll find it does

the simplest way of illustrating this is to push your bike up against a brick wall (or apply the front brake), wind on some revs and relese the clutch lever - as if strating a burn out.

Have a look at what the rear of the bike does

True... but pushing it up against a wall is entirely different to how it will react under load in a corner. You need to remember that the geometry will change under cornering forces and then it wll be in a state where the swingarm angle will indeed cause it to squat. You're also ignoring weight transferance.

Rule of thumb... chain drives squat, shaft drives lift. My TRX has a chain and it squats. Or at least it used to.

you'ld think that, but it's not. The rear rises under acceleration but it feels like squatting because the front rises more due to weight transfer

(taking away undulations / changes in camber etc) your geometry should not change during cornering - surely that's the whole point of sorting your suspension.

It WILL change under braking / acceleration but should be settled in a corner

[Beau]

you'ld think that, but it's not. The rear rises under acceleration but it feels like squatting because the front rises more due to weight transfer

Sounds rather like what I said...

Anyway, some obviously think I'm nuts, so no probs. Was just sharing a mod that was done to my bike to great effect. Not bothered if people aren't interested.

[phuk72]

you'ld think that, but it's not. The rear rises under acceleration but it feels like squatting because the front rises more due to weight transfer

Sounds rather like what I said...

Anyway, some obviously think I'm nuts, so no probs. Was just sharing a mod that was done to my bike to great effect. Not bothered if people aren't interested.

not really. I rather got the impression, through your use of the term 'squat', that you were suggesting that the suspension compresses under acceleration.

I said that the rear spring extends during acceleration.

2 completely different view points.

I am still intersted to hear what work you had done on the shock though as I'm sure many others would be.

And FWIW (and as is well known by by anyone on here who reads my posts) I run with 160 section tyres and have never had any issues with traction / stability and hold the view that 180 section tyres are nothing more than bling.

And the standard TRX swingarm is more than stiff enough as standard - a YZF arm is nothing more than a braced TRX arm

[HansJ]

...
Anyway, some obviously think I'm nuts, so no probs. Was just sharing a mod that was done to my bike to great effect. Not bothered if people aren't interested.

Not at all, it's interseting to hear different thoughts/solutions! Just curious to understand what You've done, and glad that it helped you! It's a discussion forum, so let's discuss

[Beau]

you'ld think that, but it's not. The rear rises under acceleration but it feels like squatting because the front rises more due to weight transfer

Sounds rather like what I said...

Anyway, some obviously think I'm nuts, so no probs. Was just sharing a mod that was done to my bike to great effect. Not bothered if people aren't interested.

not really. I rather got the impression, through your use of the term 'squat', that you were suggesting that the suspension compresses under acceleration.

I said that the rear spring extends during acceleration.

2 completely different view points.

I am still intersted to hear what work you had done on the shock though as I'm sure many others would be.

And FWIW (and as is well known by by anyone on here who reads my posts) I run with 160 section tyres and have never had any issues with traction / stability and hold the view that 180 section tyres are nothing more than bling.

And the standard TRX swingarm is more than stiff enough as standard - a YZF arm is nothing more than a braced TRX arm

Agree with all of that. Although my bike was definitely a "squatter"... perhaps it was more about my fat arse and less about the bike? I've ridden 4 TRX's and all squatted at the back under power. (Everyone will be going out to try for themselves tomorrow!)

As for more technical info about the mods... I've reached the limit of tech knowledge. Can't really explain it much better than I have earlier.

Anyone fitted a shock with proper 2 stage compression damping adjustment?

[Tarwetijger]

NOFI (no offence intended) Beau! It 's just a really interesting discussion.
Although it is getting above my technical knowledge too.
Now that I think of it, the "widening effect" might have got worse since the suspension has been altered the last time.

[slow codger]

Beau, everybody is interested in someones point of view and how their bike reacts with a given mod. Different people on differently set up bikes will always say that theres is better than others, just look at Motogp, or WSB! They cannot ride another riders bike on their setup. As I dont ride at 100% on the road, or anything like it, and I havent used the TRX on a track mine with the 180 rear, YZF dogbones and brembo brakes is fine for what I need. Others will argue that theirs is set up perfectly for them on either road or track, and knowing Honk and Phuk from the forum I'm sure that they will have theres set up very well, both for track and road use. And Hopefully Pete will prove to us all that he can race a TRX

Dave E

[phuk72]

:And Hopefully Pete will prove to us all that he can race a TRX

Dave E

LOL - I've got no problem getting it to go fast enough it's a matter of wheher the bike will be competetive. Thunderbikes is all about power to weight (with different calculations depedning on engine configuration and capacity). I'll be racing in the open class (over 75bhp) which means I'll have 1bhp for every 1.8 kgs. So I'm aiming for a bike that weighs about 180kgs wet.

Trouble is, I'm aware Phil Read is racing the Vyrus again and Steve Jordans's SV650 is set for 90bhp and 165kgs And while I certainly wont be bothering them at the front there's plenty of other 'specials' out there ridden by experienced guys.

[dandywarhol]

Ya should be able to stuff this one phuk......................................

[honkdawillydahonk]

Trouble is, I'm aware Phil Read is racing the Vyrus again and Steve Jordans's SV650 is set for 90bhp and 165kgs And while I certainly wont be bothering them at the front there's plenty of other 'specials' out there ridden by experienced guys.

I reckon 170kg and mid-ninties BHP might be a better target for reliabilty and handling.... Should be possible with all the road shite removed!

[Beau]

Beau, everybody is interested in someones point of view and how their bike reacts with a given mod. Different people on differently set up bikes will always say that theres is better than others, just look at Motogp, or WSB! They cannot ride another riders bike on their setup. As I dont ride at 100% on the road, or anything like it, and I havent used the TRX on a track mine with the 180 rear, YZF dogbones and brembo brakes is fine for what I need. Others will argue that theirs is set up perfectly for them on either road or track, and knowing Honk and Phuk from the forum I'm sure that they will have theres set up very well, both for track and road use. And Hopefully Pete will prove to us all that he can race a TRX

Dave E

Agreed mate. I wasn't suggesting mine was better the way it's set up compared to other people's setups.... just that it's better for me and how I like it to turn and handle. I don't understand the need for a 180 rear on these things at the expense of slower steering, but that's just me.

By the way... I tried the "put it against a wall trick" and yeah, it rises at the back under throttle. Take it for a ride though and the exact opposite happens. Obviously weight transfer has a bigger impact than chain pull... on my bike at least.