RL250 Steering geometry correction

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Takhli44
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RL250 Steering geometry correction

Postby Takhli44 » Wed May 02, 2012 2:13 am

This is what I did and it works pretty well. Remove the two gussets at steering head, make 2 bars (I used square tube) long enough to reach from forks to rear of bash plate welded together at the same width as the inside of forks. Place bars between forks and clamp other end to CENTER of bash plate. Install axle to keep forks from spreading. Hacksaw just behind steering head top to bottom leaving a bit at the bottom uncut. Use come-a-long to pull axle toward bash plate. Make and shape filler strips to fill gap in frame and weld in place. Reinstall the gussets removed earlier.

I cut through top gusset. I did 3 frames at slightly diffrent angles.

As measured from center of front axle to center of lower bolt for engine mount bracket in down tube.
Frame one: 20-1/8 inches Frame two: 20-11/16 inches Frame three: 20-5/16 inches. These measurmens are with the tubes pushed up about 1/8-3/16 inch above triple clamps and forks at full extention.

All 3 worked, frame one fender would just touch fender to exhaust in certain conditions, frame two was comfortable and I use it on my spare bike, frame three I really like and use it on my main bike. Think I took out about 3 degrees and frame one had (as close as I could measure) about the same angle as a 98 Montessa. There is very little diffrence in how these frames ride but quite a lot of diffrence from stock. Also I cut a lot off the steering stops. Turning aproches that of a modern Beta.


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Re: RL250 Steering geometry correction

Postby JC1 » Sat May 26, 2012 9:20 am

I've often wondered how an RL would steer & handle in the tight stuff with a simple changing of the fork sliders, replacing the offset-axle sliders with inline-axle sliders. That would reduce wheelbase down to a much more suitable 1315-1320mm from the std 1345mm


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FM350
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Re: RL250 Steering geometry correction

Postby FM350 » Sat May 26, 2012 12:12 pm

Straight axle forks would mean increased amount of trail, and even worse handling than the already poor stock bike. I would guess the stock RL needs to be steepened by 3-4 degrees, and cutting the top tube as outlined in an earlier post is really the easiest way to do this.



JC1
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Re: RL250 Steering geometry correction

Postby JC1 » Tue May 29, 2012 12:53 pm

Yeh, I'm not for a moment suggesting that it'd be THE fix for the RLs handling ills (steering & otherwise) - just an improvement over the stocker via a simple mod, making it more comparable to its peers of the mid 70s.

For many of us frame cutting is major work, & effectively irreversible.

And there is some method to my madness. While the RL seems out of proportion almost everywhere you look, its perhaps no more so than out the front. Seems like Suzuki tried to compensate for the frisky engine by elongating the bike at the front end to curb its tendancy to wheelie.

However, the actual steering geometry specs aren't too bad (for the day):-
27deg rake; 76mm trail

Compare that to the sweet-steering TY250:-
26.5deg rake; 90mm trail

For many of us, the RL's trail is already on the bottom edge of acceptable & any less exacerbates the tendency to 'fall-in' or 'tuck under' in tight turns (which the RL's hi crank/C-of-G doesn't help).

Probably everybody agrees it needs a considerably shorter wheelbase & obviously there are several ways to achieve that.

When in NZ in 09 I noticed an RL shortened at the rear. The central downtube was cut-out below the top rear engine mount & the swingarm pivot moved forwards considerably - not unlike the MK1 Beamish. Apparently quite a few RLs in NZ were mod'd that way but that seemed to me to be creating more probs than it solved.

If you steepen the rake with std forks & triples you'd obviously get the shorter wheelbase, more weight on the front-end & quicker steering, but also end up with very little trail. Fine if you like it better that way, but 4deg less rake as suggested gives just 49mm trail. Again that seems to me to be creating more problems for many of us than it solves.

And both of those are major work. Hence my wondering how they'd go with straight forklegs. Or triples with less offset. Every mod is a compromise, but at least its simple & reversible. If I could find enough bits to complete my RL (or find a parts bike) I'd try it, along with the forks pushed up thro the triples as much as feasible.

Ideally, I'd like shorter wheelbase, slightly less rake, less offset in the triples/sliders, lower crank, better weight distribution & less angle on the swingarm (but thats another story).


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Re: RL250 Steering geometry correction

Postby FM350 » Tue May 29, 2012 5:49 pm

Altering the frame on an Exacta seems to me much much easier than finding someone prepared to make a one off set of straight yokes, and even if you can make the yokes yourself billet material required is going to be quite costly.



David Lahey
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Re: RL250 Steering geometry correction

Postby David Lahey » Tue May 29, 2012 6:34 pm

John I know that my KT250 steering became very much like a TY250 with I fitted the TY250 forks to the KT (using KT triple clamps) but in that case it not only moved the axle back, but also steepend the steering axis due to the TY forks being shorter than the KT, so there was more than just a change in trail involved. It is an easy experiment to feel the steering changes, but the mudguard hits the KT exhaust so it is not something that is practical.


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Re: RL250 Steering geometry correction

Postby JC1 » Sun Jun 03, 2012 11:31 am

Yeh I do recall that David, but it seems to me to be more suitable for an RL (if there's no clearance probs) than a KT, esp considering wheelbase. Its worth crunching the numbers & comparing the rake, trail & wheelbase specs:

For the KT, with TY forks that are 30mm shorter & in-line sliders (in the KT triples) gives:

26.7deg rake, 98mm trail & 1270mm w'base - not too far from TY steering geometry, but check the wheelbase.

For the RL, with in-line sliders & the forks pushed up thro the RL triples (as per my last post) by 22mm:

26deg rake, 103mm trail & 1305mm w'base - not beyond the realms of trials specs for the era, tho not ideal.

Better with RL sliders & other triples readily available (& in my shed) that are easily swapped:

26deg rake, 92mm trail & 1315mm w'base,
& other combinations:
26deg rake, 85mm trail & 1320 w'base

Those 2 are decent specs for the era.

All 3 options for the RL have the benefit of shorter w'base, quicker steering, lower crank (w little loss of ground clearance), & better weight dist'n on the front - with no great expense or frame cutting/shutting. Worth a try in my view.


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Re: RL250 Steering geometry correction

Postby FM350 » Sun Jun 03, 2012 5:36 pm

Take a look at the geometry and fork layout of a modern bike. Spending an hour altering the steering angle to within about 1.5 degree of whats used on a modern machine, will work a whole lot better than fitting straight axle forks, which in most case will mean the handling is going to be worse than with OE leading axle. The main reason for altering the steering is to put more weight on the front wheel, and while fitting shorter forks or different yokes will make a difference, it wont be much, as in most cases the amount it will need to be altered for best possible handling is 3-4 degrees.



JC1
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Re: RL250 Steering geometry correction

Postby JC1 » Wed Jun 06, 2012 11:41 am

Hey Einstein, how often you just don't get it. Doesn't stop you trying to 'enlighten the world' tho!


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FM350
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Re: RL250 Steering geometry correction

Postby FM350 » Wed Jun 06, 2012 4:01 pm

Doesnt take Einstein to be able to use a hacksaw and make a couple of simple welds with a MIG set.................




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