What an oversize top tube does is to stiffen up the main triangle of the bike - mosty stresses in a top tube (and the down tube) are torsional (twisting ones) and a larger diameter is the most effective way of increasing the stiffness of these tubes. THis why most recent (built since 1990 or so) steel frames feature 1 1/8in top tubes. It is particularly important in larger frame sizes where the longer tube lengths make for frames less stiff than their smaller cousins. Steering accuracy (not response, speed etc) is imporoved by stiffening the front triangle of a frame or by making the fork bladesstiffer in a lateral (sideways) direction. Lugs contribute almost nothing to a frame's stiffness. Indeed fork trail, fork offset and head angle as well as weight distribution all contribute to a bike's handling qualities but steering accuracy depends to a large extent on the torsional stiffness of the front triangle and on the lateral stiffness of the fork blades. There is a rreal noticeable differnce between frames using 1 1/8in top tubes and those using 1in TTs. Additionally lack of front triangle stiffness is a major contributor to frame shimmy - which is why larger frame sizes are more prone to shimmy than smaller ones.
Hilary Stone, Bristol, England
> From: <vergrandis@tesco.net>
> Date: Wed, 24 May 2006 19:34:39 +0100
> To: <classicrendezvous@bikelist.org>
> Subject: [CR]Re: eBay Rensch
>
> Dear Ken,
> Many thanks for the kind letter and you comments and questions. Hoxton is
> indeed Rensch/Paris territory its boundaries are Balls Pond Road where Kamf,
> Condors and Rensch were once located, Kingsland Road where Waller was
> situated, Old Street where Harry Rensch had a shop pre-war and Upper Street
> where Macleans once were. A fifties cycling paradise!
> Paris's last proper shop and works were in Stoke Newington Road which is The
> Great Cambridge Road or A10 as it is known. As you leave the City of London
> close to the Barbican where Hobbs once was before being bombed out in the
> Blitz you enter Bishopsgate close to the famous Petticoat Lane street market
> and Brick Lane famous for secondhand bikes. This area is Spitalfields where
> the old flower, fruit & Veg market once was. Now a very trendy and expensive
> part of London. Sorry it goes Bishopgate, Kingsland Road then Stoke Newington
> Road cycling northwards towards Cambridge. Lots of famous Victorian cycling
> pubs on this road.
> All the famous names were once close to this area Ephgrave, Hetchins and
> Hanlons etc. Too many to mention.
> Norris is a wonderful chap and I always read his postings with gret interest.
> He is very knowledgeable and a great authority on the British cycling scene.
> If Norris says Paris's last shop was in Hackney his information will be spot
> on put your shirt on it. Neal, Nigel, Peter B and Doug are also great British
> cycling historians. I can't for the life of me remember the Hackney shop.
> Paris was never the same after Harry left, this is when I remember it in Stoke
> Newington. Jack Jones, Dusty Miller etc.
> Must say I am totally confused like you by the eBay Rensch description. How
> can an oversize top-tube effect the steering? Seems utter nonsense and
> claptrap to me. As a cyclist I have always found that the combination of head
> angle and fork offset determine the steering qualities of a bicycle.
> The oversize top tube was first used mainly by Claud Butler's and Harry Rensch
> in the late 30's on their lugless models. This was thought to help stiffen up
> these frames in the absence of lugs. Yes it would make a more rigid frame but
> steering?
> Only to happy to give you a guided tour of London if you ever make it overhere
> can even loan you a classic mount.
> Best wishes Frank.
>
> Frank Cohen Hoxton UK