Bicycle geometry. A brief look into how it effects your ride.
Ok, since I started blabbering about and ripping on the Jamis Aurora, I felt I needed to explain the geometry of a bike a little more in detail. So after some work in Photoshop, I’ve got a graphic and some more information to help in a touring bicycle search.
Head-tube angle- the angle between the floor behind the front wheel and the steering axis.
Trail- the distance between the front wheel’s center on contact point and the point where the extending steering axis line reaches the ground.
Fork Offset (rake)- the distance that the hub preceeds or follows the steering axis.
Let’s look at the graphic to put it all together.
The shaded green thing is the fork. Remember, the bigger the trail, the more stability. Small variations in any of these angles can have a serious impact on your ride. Larger trail figures will give you more stability, but steering precision is compromised. Longer wheelbases make turning more difficult than shorter wheelbases. Your touring bike will have a long wheelbases, so don’t expect precise turning. Your ideal touring bike should also come with a low bottom bracket, which keeps your weight closer to the ground, making it take less effort to move your body from side to side.
Plug all your specs into this website calculator…check the ACTUAL TRAIL CALCULATOR
Unless I hear otherwise, use 12.25 as the tire radius, that is for a 700 c tire.
Choosing a touring bicycle; Jamis Aurora
For our 5th touring bike option we have for you the Jamis Aurora. The 2008 model is surprisingly cheap, and this bike comes in at lower portion of the bottom price bracket and has some great features worth checking out.
At NUMBER 5… the Aurora from Jamis. Please comment if you have ever ridden, owned, or know anyone who owns this bike. Email photos of your setup to me at firstname.lastname@example.org and have them posted on this site.
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Frame- Reynolds 520 Steel
Chainstay Length- 440mm or 17.32 inches
Brakes- Tektro Oryx cantilever
Tires- Vittoria Randonneur 700×32c
Hubs- Shimano Tiagra 36h
Weight- 27 pounds
The Jamis Aurora is a pretty bike, I love the paint job. But upon further investigation we’ve found some less than attractive things appearing. A lot of these issues all combine and hinder the bikes ability to handle well under heavy loads. We will put a post up to explain this in more detail later, but basically, the geometry of the Aurora differs from a lot of the other bikes you’re going to find on the market. Now for some, this might not be a major noticeable difference, but for others it might be. Take the bike out and test ride it with other bikes and see if the handling is good for you. The issue with the Aurora is its front-end geometry and short wheelbase. Rake and Trail are fork/wheel measurements that are involved with the headtube angle, wheel and bike stability. I will post diagrams later, but here is the idea; more rake=less trail=less stability. So let’s look at the numbers of some large bikes that are popular and compare.
Trail Measurements based on stock wheels:
Jamis Aurora—– 2.19″
Surly Long Haul Trucker—- 2.37″
Trek 520—- 2.3″
Cannondale Touring 1—-2.31″
May or may not be an issue for you. As I said, test ride, test ride, test ride. This combined with the shorter wheelbase/chainstay might be enough to knock this down to the bottom of my favorites list. A shorter wheelbase would improve handling, but this is a touring bike, and we are looking for foot clearance.
Compare the price of the Aurora to other models in this range, such as the Surly Long Haul Trucker, and I wouldn’t recommend it. There have been some issues with frame construction quality, especially threading issues and from reviews I’ve read and word from the LBS.
How are ratings calculated?
Notes. Value rating is a little low because of necessary upgrades, which are similar to those I would make on the Long Haul Trucker. The quality of the bike has come under some questions regarding the quality of the steel frame, especially the braze-ons and threads. The Aurora does come pretty ready to tour with braze-ons for fenders and racks. The gearing is a little high, but not horrible.
We’ll be compiling all of the ratings on a new page, look for it to be complete shortly. Check it out here