Frame size vs wheelbase

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pq
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Re: Frame size vs wheelbase

Post by pq »

I had a Roberts road frame built many years ago. I told him I expected it to have toe overlap, not becasue I want toe overlap but becasue I knew that if it didn't, the front centres would be too long and I would hate it. Unfortunately he ignored my instructions and built it without toe overlap. It steered like a barge and so I didn't even ride it for a full season. Cue massive argument with Roberts who eventually and reluctantly agreed to turn it into a winter bike, which I have to say I'm still not too fond of. It's replacement, a very very fancy American made Ti frame bought second hand on ebay is still my daily rider after the best part of 20 years. It has huge toe overlap and handles beautifully.

The point of all this is to say that front centres make a difference, at least to me.
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

pq wrote: 26 May 2021, 8:55pm I had a Roberts road frame built many years ago. I told him I expected it to have toe overlap, not becasue I want toe overlap but becasue I knew that if it didn't, the front centres would be too long and I would hate it. Unfortunately he ignored my instructions and built it without toe overlap. It steered like a barge and so I didn't even ride it for a full season. Cue massive argument with Roberts who eventually and reluctantly agreed to turn it into a winter bike, which I have to say I'm still not too fond of. It's replacement, a very very fancy American made Ti frame bought second hand on ebay is still my daily rider after the best part of 20 years. It has huge toe overlap and handles beautifully.

The point of all this is to say that front centres make a difference, at least to me.
Do you know head angle and fork offset for these bikes?
pq
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Re: Frame size vs wheelbase

Post by pq »

The Roberts, not after all this time, no. The one I like is a Merlin Extralight, it's such a classic the geometry will no doubt be around somewhere. But the same applies to every race bike I've ever owned. The ones I like have toe overlap, which actually has been every single one bar the Roberts.

Bt the detail isn't my point. Someone said that they can't tell the difference on this thread. I very much can.
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

Its not "detail".
The major determinant of how a bike handles is trail.
Comparing 2 bikes with the same trail, I can't detect any difference plus or minus 15mm front centre.
You are "comparing" bikes with unknown trail, and jumping to the conclusion that the differences in handling are due to something which you can see, ie. toe overlap. The "comparison" is unsound; it would be just as logical to say that differences in frame colour account for the differences in handling.
I suspect that you prefer the handling of low trail designs, and I know that under some circumstances it is impossible to build a low trail frame; typically its impossible to build a small low trail frame with toe clearance using standard offset forks.
pq
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Re: Frame size vs wheelbase

Post by pq »

Yes, I absolutely do prefer bikes with low trail, at least for riding on road without panniers - classic race geometry. Both these frames were supplied new with carbon forks, the Merlin with 45mm and I'm fairly certain the Roberts too. Certainly the Roberts now has 45mm forks and it handles the same as it did before. The top tubes are roughly the same length and the cranks identical, so the difference between the two bikes must be the head angle. Or the colour. The Merlin is unpainted, the Roberts blue, or "burnt orange" according to the build sheet.
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

If the offset and wheel size are the same, and they handle differently, the conclusion is unavoidable; the head angle is different.
Maybe Roberts were making a point that it is possible to build it without overlap. There are riders who would prefer slow steering and no overlap to quick steering with overlap, but thats something which should be established before building it!
Philip_Rogers
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Re: Frame size vs wheelbase

Post by Philip_Rogers »

531colin wrote: 24 May 2021, 7:05pm
GuyBoden wrote: 24 May 2021, 4:59pm I've been comparing some Spa Cycles frame size and wheelbase.

(In descending order.)

Sabbath Silk Route, Wheelbase 1045 for 54
Spa Elan, Wheelbase 1047 for 54
Spa Tourer, Wheelbase 1071 for 54
Spa Wayfarer (Long), Wheelbase 1088 for 54
Spa Roughstuff, Wheelbase 1093 for *53*
You can add to that D'Tour 54 @ 1086

Road bikes have short wheelbase for quick steering and "responsiveness" allegedly. (and also to allow a fashionable long stem)
Touring bikes have long chainstays for pannier/heel clearance, and clearance at the front for mudguards, sensible tyres and your feet.
When you are slithering down some steep and dodgy track with everything you need for a couple of weeks on board, its very comforting to have the front wheel "out in front" rather than underneath you like it is on a road bike.

I don't really think about "wheelbase" as such, but I do think about its component parts, front centre and chainstay.
I'm still not sure what you are looking for?

Colin

I've been mulling over replacing my Hewitt Cheviot SE XL frame with a ti equivalent. I've always fancied Ti and my wife has a VN Amazon ladies which has proved durable.

Please could you coment on any differences between the Sabbath Silk Route and Spa Ti Touring frame. The geometry on Spa's webpage is similar but slightly different. I'd be looking at a large or XL size.

Thanks :)
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

Hi Philip

I was already retired from Spa when they took over the Sabbath bikes, so I was never directly involved with them, but I have compared the 60 cm size of both bikes "by the numbers". My advice would always be to phone up and check that Spa have test bikes in sizes you are interested in, and go get a ride.

My overall impression is the Sabbath is a more "racy" bike than the Spa.
In round numbers, the sabbath chainstays are 20mm shorter, front centre 15mm shorter, wheelbase 40mm (ish) shorter
head tube 30mm shorter, although both have steel steerer so you can have as many spacers as you like, and the sabbath 60 actually measures 580mm seat tube. (Spa measures 600)
Very little in top tube length, sabbath is about 5mm shorter. BB height the same...........Correction....about 10mm higher on the Spa with the same tyres
Seat tube angle is 73 degrees on the Sabbath, only 1 degree steeper than the Spa, but I would struggle to get my Brooks saddle far enough back.
Steering geometry is different; the Sabbath was designed to take a Surly Trucker fork originally, and so its 45mm offset and 72 degree head angle. ....this is much the same as the Spa Audax and Sabbath September. The spa tourer steering is designed to be relatively unaffected by road camber, side-winds, luggage, or me looking at the view rather than where I'm going.....some will find the steering "barge-like".

I would say if you want a bike with an involving ride for day rides and credit card touring, get Sabbath.
If you want to go bridlepathing or camping get Spa.
Jamesh
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Re: Frame size vs wheelbase

Post by Jamesh »

Thanks Colin helpful post.

73° makes a difference

I always thought

72 touring, 73 race / audax, 74 time trial

Are frames best when parallel? I.E. 72/72 etc???

Cheers James.
Last edited by Jamesh on 25 Sep 2021, 3:57pm, edited 1 time in total.
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

Jamesh wrote: 24 Sep 2021, 6:38pm ...........Are frames best when parallel? I've 72/72 etc??? ..........
No, they are best when the seat tube angle is set so the rider can get the saddle where they want it, and the head tube angle so the steering characteristics are as the rider wants.
Doesn't sound difficult, does it? but then you have fashion, which means that if you want to sell bikes you have to make them (look) fashionable.
So we all have to put up with fashionable steep seat tube angles, which sends people scurrying off to find seatposts with a long layback; I would be quite happy with seat tube angles say 70 degrees....1 degree is worth about 10mm of saddle fore/aft for somebody of "average male height" so I could easily get my saddle where I want it, and somebody wanting a forward saddle position could use an in-line seatpost....plenty of them about, last time I looked.
And if you want a carbon fork, then you can have 45mm offset and lump it, because thats the offset most used on (pretend) race bikes. Which is fine if you are average male height or taller and either don't want mudguards/big tyres or don't mind toe overlap. Of course most people less than average male height are female.....https://www.stevehoggbikefitting.com/po ... ve-issues/.....theres a part 2 to that, as well. and despite the later note that forks with different offset are becoming available, thats available to the big hitter manufacturers, not available to every Joe at commodity prices.
Philip_Rogers
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Re: Frame size vs wheelbase

Post by Philip_Rogers »

Hi Colin

Many thanks for the helpful reply. I can see some of these issues. I'm 184cm tall, but long body and arms for my legs, and use a B17. Getting seat postition right needs a layback seatpost and long stem / reach, but lower saddle than for the average person of my height.
A trip to Spa in due course may be the way to go. I'm almost tempted to start from scratch with a new Elan which would give me discs.
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

A visit to Spa should always include a ride on an Elan.
I was coming up to 70 when I designed the Elan, and I was fairly resolute that I didn't want disc brakes. After all, I could do anything I needed to do on Vee brakes, in the dark, and with cold hands.....why did I need to learn a whole new brake?
But the damned thing just rides so nice.....I kept borrowing the test bike, in the end I had to have one.
There is a line in the bike details "If it doesn't put a grin on your face, don't buy it." I wrote that, and I stand by it.
I don't know if you want to go camping, it might be a bit of a handful with 4 panniers, although there may be people on here who have done it!
MikeF
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Re: Frame size vs wheelbase

Post by MikeF »

531colin wrote: 25 Sep 2021, 3:14pm
Jamesh wrote: 24 Sep 2021, 6:38pm ...........Are frames best when parallel? I've 72/72 etc??? ..........
Of course most people less than average male height are female.....
True but as half of men (assuming a normal height distribution) are less than average height, most people in total are less than male average height.
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
Jamesh
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Re: Frame size vs wheelbase

Post by Jamesh »

531colin wrote: 28 Sep 2021, 5:58pm A visit to Spa should always include a ride on an Elan.
I was coming up to 70 when I designed the Elan, and I was fairly resolute that I didn't want disc brakes. After all, I could do anything I needed to do on Vee brakes, in the dark, and with cold hands.....why did I need to learn a whole new brake?
But the damned thing just rides so nice.....I kept borrowing the test bike, in the end I had to have one.
There is a line in the bike details "If it doesn't put a grin on your face, don't buy it." I wrote that, and I stand by it.
I don't know if you want to go camping, it might be a bit of a handful with 4 panniers, although there may be people on here who have done it!
Just been looking at the Spa elan is the titanium model worth the extra over the 725 model?
The ultegra group is an draw esp for big birthday bike ..

Just thinking aloud for a few years time!

Cheers James
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531colin
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Re: Frame size vs wheelbase

Post by 531colin »

The steel one is a nice enough ride, but the Ti is shiny!
I kid myself the Ti is more comfortable for somebody who is "light for the height"......but go ride them!
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