TLR 250 Steering head mods

[Gary B]

Hi,
I'm looking for some advice of changing the steering head angle on my TLR250.
I've moved my pegs down & back which helped its general handling heaps, but it still steers like the front wheel is way too far in front of the bike.
I've heard of people cutting either the backbone of the frame below the tank & pushing the top of the steering head forward to steepen the angle and other stories of cutting the down-tube below the steering head and pulling it back to achieve the same result.

Anybody know of the benefits or issues with either way?

Also what angle is right, what's too much, what's the best way to measure it ???
Reduced distance between axles ???

Any advice will be greatly appreciated.

Thanx in advance.

[Julz]

I can't answer your specific question sorry, (and it's been a while since I posted here), but have heard / read the following:
* On KT250's people used to cut the top tube and insert approx 1" of extra tube to steepen the steering angle. FredKT has suggested simply putting the frame in a press and bending it to achieve the same result (which seems risky to me, but who knows).
* While it is common to move the foot pegs down and back on most classic trials bikes, I have read somewhere that a TLR250 works better if you move them down and forward, as this helps to counter the light front end and slightly sluggish steering.
* Hope I am not opening a can of worms here, but there seem to be 2 theories about weight distribution when steering an older trials bike. Some people say you need to get your weight over the front wheel to help with traction. This seems to align with the TLR250 theory above and with people who steepen the head angle. The other way, which Mick Andrews teaches, is to get your weight right back over the back wheel and let the front end pivot around it. Having ridden a KT with it's tendency to sledge, I have personally found that the weight backwards approach has worked better for me (but I am only an intermediate rider).
* Just read the other thread on TL125 fork trail - seems you can also change the steering by replacing front end with forks that have different rake and trail...

[sharvie]

Hi Gary,

This is a tough one, A friend & I have TLR''s which are very similar spec. One of the main differences is he went ahead and steepened the steering angle. After much deliberation I left mine standard.

It would seem as though there isn't any noticeable turning advantage with the steeper angle when riding the bikes side by side.

The TLR is known to suffer from tyre plough in certain situations though.

My tip would be to concentrate on front suspension setup, make it as supple & responsive as possible in the initial part of the stroke. Also varying how much tube protrudes front the top of the fork clamps.

The steepened steering angle was based on information from the classic trial website.

Hope that helps

[yammyty]

Gary, u can measure the TRAIL of your bike setup. Leading axle does make harder or at least put variables to the comparison to other bikes TRAIL.
Measure Trail, hold bike upright run a plumb bob from axle to ground and mark it, (non leading axle) run straight edge down centre of for leg/ slider and mark on ground, measure distance (usually 7 - 8 inches).
Leading axle is same but straight edge is centred between axle and centre of tube and middle of triple clamps (1/2 way between the two) I may be wrong so if someone knows different I would like to know.
Good luck

[TriCub]

yammyty. You are wrong, have a look at the post about the TL125 one back.

[yammyty]

quote="TriCub"]yammyty. You are wrong, have a look at the post about the TL125 one back.[/quote]
I have read your post's and seem to be conflicting to what engineers consider TRAIL & RAKE .
I have posted a link to help others not get caught up in opinions.
http://en.m.wikipedia.org/wiki/Bicycle_ ... e_geometry
http://upload.wikimedia.org/wikipedia/c ... try-en.svg

[JC1]

With respect Yammyty, its not Tricub who's getting confused with incorrect opinions. George (Tricub) is correct.

On the websites links you posted, firstly they are wikipedia, which should always be taken with a 'pinch of salt' as they say. Last I heard their 'definitions' are posted by anybody who thinks he knows & wants to air his 'knowledge' - Joe Public - not by engineers or anybody with any authority. While such people may footnote experts, they don't always fully understand what those experts are saying & hence misrepresent them. It's the old problem of relying on secondary sources rather than primary sources. (And yes, there are engineers on this forum)

And secondly, probably what is confusing you, the eg there is for a bicycle where the forklegs are in line with the steering stem (even tho the axle isn't), unlike on a motorcycle where the forks are offset from the steering axis.

To find trail (whether the fork sliders have offset axle or in-line axle) you have to extend the steering axis down to the ground not the line of the forkleg. That's not easy to do accurately.

For what its worth factory specs for the TLR250 show 24.5deg rake & 78mm trail, but I'm not sure that on its own helps Gary much.


Gary I'm none too familiar with TLR250s, having only ridden one briefly & I tho't its handling was marvellous (compared to other twinshocks I'd ridden). Nor am I an above average rider (in fact, a very 'rusty' rider) but I never noticed the front wheel seemed too far 'out there', tho depending on your height I guess shorter riders may (I'm 5'10'').

I hate to say what you/others may already be thinking but it sounds like moving your pegs back may have exacerbated your problem. (It's the classictrial website that recommends moving them forward on the 250.)

Have you tried moving your bars forward &/or sliding the forklegs up thro the yokes (if you can do that on the TLR). Not many seem to realize that for every 10mm you slide the forks up you also move the front wheel back almost 5mm so if you could slide them up say 30mm (even just to try it) the front wheel would be about 15mm closer to you. (Tho this also changes rake & trail a little)


Personally I'd be wary about cutting the frame to steepen the rake (especially on a bike that already has rake & trail at the lower/'sharper' end of twinshock specs as the TLR250 does). When people do that they rarely consider the associated change in trail & its effect. (Modern bikes not only have different rake, they also have diff yokes too.) For every degree you reduce rake you also automatically reduce trail 7-8mm. In general, reducing rake gives quicker/sharper steering & reduces wheelbase, putting more weight on the front wheel (depending on how you do it). Reducing trail gives less stability (less self-centring effect) & can cause/increase the 'tucking under' effect on these old bikes if you go too far.

People often claim (eg) they "copied modern GasGas geometry", but how much geometry did they copy? Usually just the rake with little/no tho't given to the associated changes in trail, wheelbase, weight distribution, etc - all variables that affect steering/handling.
Did they really make it better, or just different!

[TriCub]

quote="TriCub"]yammyty. You are wrong, have a look at the post about the TL125 one back.

I have read your post's and seem to be conflicting to what engineers consider TRAIL & RAKE .
I have posted a link to help others not get caught up in opinions.
http://en.m.wikipedia.org/wiki/Bicycle_ ... e_geometry
http://upload.wikimedia.org/wikipedia/c ... try-en.svg[/quote]

Those Engineers must have gone to a different school or maybe they got their Diplomas from the back of a Cornflakes packet.

[yammyty]

JC1 great post, I am more than happy to be wrong if someone actually post something worth reading.

[pop]

I would try this first, move the forks up in the clamps as much as possible, run the back wheel as far forward as it will go and lower the top shock mounts by 1/2 inch.