Quick question

[steve hawkins]

What is the rake and trail on an R65?

Cheers

Steve Hawkins

[Rob Valdez 79 R65]

I will dig out some old magazine tests from the day.  I can't seem to find the numbers on the net anywhere.

[nhmaf]

According to my "Boxer from /5" history book, all twin shock R65s from 1978 - 1984 had:

Steering head angle: 63 degrees
Trail:  96mm
Stanchion/fork diameter 36mm
Wheelbase (1978-1980) 1390mm
Wheelbase (1981-1984) 1400mm

And, since you're dealing with an R100 (though I only have data for  -> 1984 twin shock models, no mono/para-levers):

Steering head angle: 62 degrees
Trail: 88mm
Stanchion diameter: 36mm
Wheelbase: 1465 mm

Because of the shorter wheelbase of the R65, having a bit more trail helps with the stability - the head angles are pretty close to the R100, so you might not have too bad of a handling change, with the combination of the leading axle forks, your trail figures wont be too far off, though raising the fork tubes a wee bit may offset the few mms of difference.  With the 1cm offset and leading axle and 1 degree angle difference, I expect that your wheelbase will "grow" a little.   I don't know if all these slight tweaks would
seriously affect your handling, I'd expect that it may make the bike a bit slower handling, particularly at low speeds - but I've done extremely little in the way of modifying bike's steering geomtery and am only speculating.

[steve hawkins]

Thanks nhmaf,

I too eventually found it, in an old Cycle World BMW road test book I had kicking around where it was quoted as 3.8 inches for an LS - which aprox 97mm.

I have seen R100's quoted as anythying from 3.5 to 3.7 inches.

I tried to measure it myself last light but was pretty bemused by it.  Although the leading axle is 3.5cm forward of the centrline of the fork, it actually makes much less difference to the trail due to the angle of the fork.  so we are talking less than a cm effect on trail - which would keep me above 3 inches trail - but with a slightly longer wheel base?

Still confusing.  However, I would gain a firmly fixed pair of forks that would be less likely to move around other than up and down.

[nhmaf]

I agree as a general rule of thumb for streetbikes, staying above 3 inches of trail is a very good idea for stability. the few extra mms of wheelbase probably won't hamper too much, but I'd expect that it would slow down the bike's handling just a tiny bit.  If the trail gets too close to 3 inches or less, I'd expect you to have twitchy problems or wobbles at higher speeds or with road irregularities.  If you do go through with these modes, many of us will be very interested in hearing how things go - just be sure to go slowly at first and don't take her out onto the M until you've racked up a number of miles on local, slower speed roads.

[steve hawkins]

Just blagged a set of yokes/stem on ebay for £25.

Should get them early next week.  Won't do the swap until the following weekend - it will give me a chance to clean them up a bit and check the state of the bearings.

I wonder what the fork offset is on a complete front end from a k series?

Cheers

Steve H

[trolle]

For those of us who are completely illiterates there is a good explanation on Wikipedia: http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry

I found this as well: http://wotid.com/tls/content/view/24/53/ which explains the mystery of counter steering as well.

greetings from a warm and sunny north - excellent driving conditions!

[Justin B.]

Steve, if you need some custom width axle spacers to get your wheel centered in your new fork arrangement let me know, I'm sure I could brew something up.

[steve hawkins]

I will probably buy an R65 axle and spacer and go from there.  

At least the length will be right.

Then I need 10mm with of spacers for the disc......

If I have time this weekend I might remove the front wheel off my R65 and offer up the axle to the R100.  I am aware that there are axle differences with the earlier models, but I am not sure about these two specific models.  

By the way, what makes the wheel base of a post 81 R65 differ to a pre 81 R65?

Cheers

[nhmaf]

I am not sure, but thought that it might be the difference in the offset up at the fork yoke - didn't you see a 1cm difference between the R100 and the R65 yoke you have ?   I am thinking that maybe the pre-1981 R65 models used the same yoke as the R100/7 of the same period ?

I haven't found anything else to explain it, but this is what is printed in my text book on the airhead series history.   It might be in error, but it is correct on many things I've checked thus far.

[Justin B.]

I have an '80 and I can say for certain the top yoke is not R100ish, it is an aluminum casting like the post '81s...

[steve hawkins]

Yes,

     all r65's have the same aluminium yokes I believe.  You might find they changed the head angle form 27 to 28 degrees - something that would be difficult to spot.  Who knows?  It might even be that two different people measure the wheelbase at two different times and got two different measurements.  

As for the R100 - 'Widow maker' - which will be blacked up soon (already has a satin black front wheel).

I am just securing an R65 axle and spacer (£6) to help resolve the issue of the wider R65 yokes on the R100 - I am not sure yet whether I will have to do any machining yet.  But the spacing out of the brake calipers is easy as they just need a couple of 5mm spacers each side.

Could be on for a trial soon.  Ooer!  3 inches of trail!

Cheers

[Jon_P]

you should be ok steve, good trails numbers are 3" to 7"

less than 3" you would be in a world of hurt at high speeds but it would handle great at slow speeds. more than 7 is just the opposite, handles real bad and wants to flop over at slow speeds and will want to go straight at high speeds which is a bit of a problem when hitting the twisties.