Rivendell Relaxed Rear Geometry & Actual Effect

[John Hawrylak]

A relaxed rear geometry seems 1 major feature of all Rivendells (except the Roadeo), i.e slacker Seat Tube Angles (STA)are used compared to other frames, whether large or small builder.  The STA angles of the small to medium frames vary from 71.5 deg (Sam, Joe A, San Macro) to 72.5 deg (AHH, Atlantis, Ram) which are less than:

• Small 27"/700C frames which typically have steeper STA, 73 to 74 deg, to avoid toe clip overlap.  The exception being a long top tube, requiring shorter stems to maintain reach within limits
• Larger frames even are less than 73 deg, a typical British STA. 

The slacker STA puts you further back, 6 to 18mm, depending on the STA compared to 73deg STA. 

My questions to the group

 

1.  Is the relaxed rear geometry something you can feel when compared to other frames??

2.  Do you see it as a positive?? 

The relaxed rear seems to go together with the higher head tube, bars up to saddle height and further back, which also seem to differentiate Rivendell, assuming lugs & great paint jobs don't affect the ride. 

John Hawrylak

Woodstown NJ

 

[Steve Palincsar]

On 12/23/2015 07:32 PM, John Hawrylak wrote:

A relaxed rear geometry seems 1 major feature of all Rivendells (except the Roadeo), i.e slacker Seat Tube Angles (STA)are used compared to other frames, whether large or small builder.  The STA angles of the small to medium frames vary from 71.5 deg (Sam, Joe A, San Macro) to 72.5 deg (AHH, Atlantis, Ram) which are less than:

• Small 27"/700C frames which typically have steeper STA, 73 to 74 deg, to avoid toe clip overlap.  The exception being a long top tube, requiring shorter stems to maintain reach within limits
• Larger frames even are less than 73 deg, a typical British STA. 

The slacker STA puts you further back, 6 to 18mm, depending on the STA compared to 73deg STA. 

only if you ignore the fact that you can slide the saddle back and forth within the range allowed by the seat rails

My questions to the group

 

1.  Is the relaxed rear geometry something you can feel when compared to other frames??

2.  Do you see it as a positive?? 

STA is one component of saddle position.  Seat rail length and seat post setback are two others.  The big deal with Riv STA is that the most common saddles used on those bikes, Brooks B.17s have very short rails, and if you like to have the saddle fairly far back it's hard to get there with most seat posts unless you have a slack STA due to insufficient seat post setback to make it happen.  You really don't "feel" the affect of STA other than in your ability to get the saddle where you want it, and if you can that's a distinct "positive".

[Don Compton]

I think more significant  geo numbers are front to center and the chain stay length. They are a big part of Grant's bikes wonderful handling.

[Marc40a]

I compensate for the slackened STA of my Hillborne with a zero setback seatpost.

Your figures correlate with mine.... Approx 6mm difference for each half degree of setback, if I remember correctly.

As to whether the relaxed geometry is a positive or a negative, I don't think of it that way . Maybe I would if I couldn't position myself where I needed to be on the bike (assuming I had the correct frame size). I look at the bike's design as a whole because changing one aspect of the geometry would undoubtedly affect others. The bottom line for me is that my bike feels amazing and I have the fit really dialed in.

[Garth]

Yes, every change makes for a completely different bike !  No matter how small. No 2 of anything are ever alike , even the same model built by the same person to the same specs. etc. etc. 

[William deRosset]

>1. Is the relaxed rear geometry >something you can feel when compared to >other frames??
>
>2. Do you see it as a positive??

Hello,

1. It is not noticeable as long as the saddle position can be obtained. It is one ingredient in bike fit.

2. In my case, I like a fair bit of setback, and Brooks saddles, which require additional setback as well. I visited the Alex Singer shop in 2011, and Olivier, the proprietor, pointed to my machine's (72.5 degree) seat tube and said, "That is too slack." The (plastic) saddle was centered in its adjustment range, and I needed every bit of that extra 7mm (and a high-setback seatpost) to use a Brooks Professional. My Alex Singer had been built with a 74deg seat angle, and I did not ever really work out the position on it for long distance riding.

Best Regards,

Will

William M deRosset
Fort Collins, CO

[Utah]

The slack seat tube works together with the slack headtube which you can definitely feel! 

[masmojo]

It occurs to me that having a slack STA is probably necessary in situations where you have fewer frame sizes (like the Clem/Clementine) because as the seat post is raised it opens up the effective top tube distance allowing the frame to accommodate a broader range of riders.